1. Field of the Invention
The present invention relates to an optical communications system for communications between a base station and remote stations.
2. Description of the Related Art
Among the network architectures for optical communications systems is a passive optical network (PON) architecture, in which a base station supports a plurality of remote stations and, it is applied when the communication capacity of each remote station is not too large, to inserting an optical divider/coupler in an optical fiber connected to the base station for accommodating two or more remote stations. The PON architecture is broadly classified into two types: bus networks and star networks.
With the bus networks, downstream optical signals sent over a trunk optical fiber are branched in couplers for distribution to remote stations. Each upstream optical signal output from each remote station is combined in each coupler with the trunk optical filter for transmission to the base station.
With the star networks, optical signals from the base station are distributed through an intermediate star coupler to remote stations. Optical signals from the remote stations are combined in the star coupler and then sent to the base station.
As described above, the bus networks are suitable for a situation in which each of the remote stations is arranged in a line along the trunk fiber. In some instances, it is desired to allow a single trunk optical fiber to accommodate more remote stations than the bus networks. In that case, one might suggest connecting a star coupler to the trunk optical fiber; however, this approach would require installation of new optical fibers for connecting the remote stations to the star coupler, thus resulting in failure to make good use of the advantage that the remote stations are arranged along the trunk optical fiber.